The resulting data is divided into several segments

[7571deng]

[FengChendian]

No \0 in your string. It's possible to truncate your string due to windows API. And the API is designed that it will return the read data when win32 function returns the sending is complete (Maybe I/O just delay). So readBytesSize may be less than bytesSize.

You can increase dataPollingInterval to wait data io is complete.

Or use readBytesUntil function. The function waits flag string in endless loop;

ReadIntervalTimeout is useful for this problem. https://learn.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-commtimeouts

  void readBytesOnListen(int bytesSize, Function(Uint8List value) onData,
      {void onBefore()?,
      Duration dataPollingInterval = const Duration(microseconds: 500)})

I think I should add wait until bytesSize is ready parameter to fix this problem in readBytesOnListen. I will publish the change in next version.